It is 8:14 p.m. on a recent Thursday during the National Symphony Orchestra season, and Kevin Delaney is standing in a tiny booth at the Kennedy Center. He signals those radio stations standing by for live broadcast of the concert. "This is Mutual Broadcasting, we are about to test for phasing," says Delaney, the show's producer and director. In a booth next to his, Paul Teare, the program director of WGMS-FM/AM (103.5/570), takes a last glance at his script for the night's performance of Verdi's "Requiem."

Hours earlier Edward Kelly, a freelance engineer, had supervised the hanging of the 14 microphones around the concert hall stage. He is now at his mixing board. A music director thumbs through a copy of "Requiem."

When all the stations are on line, the broadcast starts. In a calm, almost hypnotic voice, Teare announces the program, talks about Verdi and describes the vista of the hall. Delaney directs Kelly to up the volume of the "audience ambiance" -- clapping, rustling of programs, talking. Unbeknownst to him, Delaney's microphone is still live as he begins double-checking with a technician at Mutual's Crystal City studio over the first line of Teare's introduction. Teare would say later that the exchange wasn't heard. However, as the orchestra starts, a heated discussion about the snafu erupts in the soundproofed area. The rest of the evening goes smoothly.

Mutual started these broadcasts three years ago, the first regular symphony concerts on commercial radio since the Toscanini classics. Now 51 stations subscribe to the satellite feed, reaching an audience of 1.3 million listeners at any time during the two-hour concerts. Eight of the 13 broadcasts are live, and five are post-produced.

"It's thrilling," says Delaney, who produces President Reagan's weekly broadcasts and specials such as Monday's Country Music Association Awards. "And it gets easier because you know the players, you know where to get things done. But it stays as hard as it does because of the nature of the live broadcast."

Teare, the host since the inception of the series, finds the work enjoyable but not always easy. "I have traveled with the orchestra to Europe, South America and the Far East, so some of them are personal, close friends, and I am able to infuse a personal note," he says. He spends about two hours working on each script.

"The hardest part is the five minutes before we actually go on the air," says Teare. "I get nervous, because the element of surprise is truly there." Last week, for example, the performance began two minutes late, but Teare was able to ad-lib about Verdi. "Sometimes when I have had to be spontaneous, I have gone to describing who is in the audience -- the Spanish ambassador, the Greek ambassador," he laughs.

Tonight there is no intermission, so Teare takes a long cigarette break and chats with an NSO administrator about future programs and personnel. At 9:10, well before the conclusion of the concert, he starts preparing for the postconcert interview with Henry Fogel, executive director of the symphony. When the orchestra stops, Teare talks enthusiastically about the performance until Fogel arrives. When he slips into the extra seat in the booth, the evening ends with a friendly chat.